The overall objective of these studies is to develop a better understanding of the mechanism and control of DNA replication in the F1 sex factor and related plasmids such as the drug resistance determining R factors. The synthesis taking place during conjugal DNA transfer as well as the vegetative replication of the plasmids will be investigated. More specifically, we hope to determine on F1 the origin of transfer, the origin and direction of vegetative replication, and the location of the break in the relaxation complex of F1; and to compare these positions to see if they are common or separate sites. The major methods to be used include centrifugation, electron microscopic examination of heteroduplexes and partially denatured molecules and the cleavage and mapping of fragments produced by RI restriction endonuclease. Other studies will be concerned with the characterization by centrifugation, hybridization and electron microscopy of the intermediates present during the vegetative and transfer replication of F1. We will also attempt to determine whether plasmids such as ColE1 without sex factor activity are transferred by a unique strand mechanism characteristic of the self-determined transfer of F and R factors.